I have the Bill Liebcap vacuum system on my Ikelite housing. The vacuum keeps it closed even if the latches are not done up. And the warning lights let me know if there is a leak.
The warning lights are important. I had vacuum sealed my housing, went for a dive and noticed moisture in the housing, The lights warned me. A slight crack in the dome, where the dome was cemented to the base was letting in a slight amount of moisture.
I, at first thought it was condensation but the salt crystals surprised me. Leak is now fixed.